Sexual Dimorphism (was Re: Ornitholestes)

["Andy Farke" <andyfarke@hotmail.com>]

----- Original Message -----
From: "Jordan Mallon" <j_mallon@hotmail.com>
> >From: StephanPickering@cs.com
>
> >Dilophosaurus's two species, moreover, may be sexually dimorphic
> >representatives, crested females to attract males (in this case, males
> > >being the crestless forms known as Liliensternus) -- speculation, to
>be
> >sure, but more viable than the heterosexist filters one encounter
>(e.g.,
> >the gaudily frilled ceratopsians are often described as "male" >to entice
> >females; this is nonsense: ceratopsians were female->dominated).
>
> Hmmm... I'm not so sure about this.  Respected listmember Rob Gay has been
> looking into sexual dimorphism as it pertains to _Dilophosaurus_ and
hasn't
> yet found any sign of this condition in this genus.

It is *extraordinarily* difficult to confirm sexual dimorphism in extinct
animals, especially without a monospecific bonebed accumulation (as Rob
discovered with Dilophosaurus). For instance, I am suspicious of any claims
of sexual dimorphism in Tyrannosaurus. Yes, it looks very convincing when
you place bones side by side. However, the sample is still quite small, and
stratigraphic and temporal data are minimal for many specimens (even
recently collected ones). Even if specimens are "only" two million years
apart, it is possible that they belong to different species, rather than
sexual dimorphs. In all, we have frustratingly little data on the
stratigraphic placement of most well-collected Hell Creek dinosaur specimens
(Triceratops, Edmontosaurus and Tyrannosaurus, for example). <stemming rant>

Andy
_______________________________
Andrew A. Farke
South Dakota School of Mines and Technology, Box P404
501 East St. Joseph Street
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605-394-2816

andyfarke@hotmail.com